Feb. 1832. st, Paul's rocks. 9 



and glossy, and has a pearly lustre ; it is considerably harder 

 than calcareous spar, although it can be scratched by a knife : 

 under the blowpipe it decrepitates, slightly blackens, and 

 emits a fetid odour. It consists of phosphate of lime, min- 

 gled with some impurities; and its origin without doubt is due 

 to the action of the rain or spray on the bird's dung. I may 

 here mention, that I found in some hollows in the lava rocks 

 of Ascension considerable masses of the substance called 

 guano, which on the west coast of the intertropical parts of 

 South America occurs in great beds, some yards thick, on 

 the islets frequented by seafowl. According to the analysis 

 of Fourcroy and Vauquelin, it consists of the urates, phos- 

 phates, and oxalates of lime, ammonia, and potash, together 

 with some other salts, and some fatty and earthy matter. I 

 believe there is no doubt of its being the richest manure which 

 has ever been discovered. At Ascension, close to the guano, 

 stalactitic or botryoidal masses of impure phosphate of lime 

 adhered to the basalt. Tlie basal part of these had an earthy 

 texture, but the extremities were smooth and glossy, and 

 sufficiently hard to scratch common glass. These stalactites 

 appeared to have shrunk, perhaps from the removal of some 

 soluble matter, in the act of consolidation ; and hence they 

 had an irregular form. Similar stalactitic masses,* though I 

 am not aware that they have ever been noticed, are, I be- 

 lieve, by no means of uncommon occurrence. 



We only observed two kinds of birds — the booby and the 

 noddy. The former is a species of gannet, and the latter a 

 tern. Both are of a tame and stupid disposition, and are so 

 unaccustomed to visiters, that I could have killed any num- 

 ber of them with my geological hammer. The booby lays her 

 eggs on the bare rock ; but the tern makes a very simple nest 



* I may mention that I was shown, at Ascension, some very fine 

 stalactites, composed of sulphate of lime, w^hich had been taken out of a 

 cavern. From their external appearance they would generally be mistaken 

 for the ordinary calcareous kind. It was interesting to observe, in a frac- 

 tured specimen, the double cleavage intersecting with its even planes, the 

 irregular layers of successive deposition. 



